Iranian Oil Minister Bijan Zanganeh said on Saturday frequent U.S. comments about oil prices had created market tensions.

U.S. President Donald Trump, who has made the U.S. economy one of his top issues, has repeatedly tweeted about oil prices and the Organization of the Petroleum Producing Countries. He has expressed concern about higher prices, including last month and ahead of OPEC’s meeting in December.

“Americans talk a lot and I advise them to talk less. They (have) caused tensions in the oil market for over a year now and they are responsible for it, and if this trend continues, the market will be more tense,” SHANA quoted Zanganeh as saying.

U.S. crude futures briefly hit a 2019 high on Friday but later retreated along with benchmark Brent oil as worries about the global economy and robust U.S. production put a brake on prices.

OPEC and its allies including Russia, an alliance known as OPEC+, agreed last year to cut production, partly in response to increased U.S. shale output.

Washington granted waivers to eight major buyers of Iranian oil after the U.S. reimposed sanctions on Iran’s oil sector in November, after withdrawing from the 2015 Iran nuclear deal.

“We do not know whether U.S. waivers would be extended or not, we will do our job but they (the U.S.) say something new every single day,” Zanganeh said.

Zanganeh was speaking at a news conference ahead of the planned inauguration on Sunday of four development phases at South Pars, the world’s largest gas field, by President Hassan Rouhani.

He said Iran had invested $11 billion to complete the phases 13 and 22-24 of the giant field, which Tehran shares with Qatar, and expected to operate 27 phases by next March, SHANA reported.

France’s Total and China National Petroleum Corp (CNPC) suspended investment in phase 11 of South Pars last year after the United States threatened to impose sanctions on companies that do business in Iran.

But Zanganeh said talks with CNPC were continuing.

“Negotiations are ongoing. A senior delegation from China is due to come to Iran for talks. They have promised to come to Iran soon,” said Zanganeh.